This invention relates generally to light emission microscopics as used in semiconductor device testing.
Defects in Semiconductor chips exhibit a LED effect and emit cold radiation with a wavelength of 0.4 xcexcm to 1.3 xcexcm. Traditionally Emission Microscopes have detected radiation emitted from semiconductor chips in the wavelength regime of 0.4 xcexcm to 1.1 xcexcm, and have been used for finding defects in semiconductors.
This invention is directed to extending the range of detection of Emission Microscopes to the 2.2 xcexcm range. By detecting longer wavelengths the Emission Microscope becomes capable of detecting heat emitted from semiconductor chips. This obviously requires using detectors which are sensitive to wavelengths up to 2.2 xcexcm, and using lenses which will operate in that regime. However the Emission Microscope also becomes sensitive to the parasitic thermal radiation emitted within the Microscope and other optical components, and these parasitic thermal signals dramatically degrade the sensitivity of the system. Infrared Microscope Systems exist which try to overcome the problem by one of two ways. First cooling the optical components reduces the parasitic thermal radiation which impinges on the detector. Alternately heating the chip makes it emits more thermal radiation, which overcomes the parasitic thermal signal emitted within the optics. In either case the chip temperatures detected will be significantly higher than the temperature of the optical components. Cooling the optics is messy because it leads to moisture condensation and frost formation on the optical components, and thus all the cooled components have to placed inside a hermetically sealed vacuum chamber. This severely constrains the kind of optical components which can be used and limit the useability of the system. Heating the semiconductor chip is inconvenient and slows down the analysis, because a special fixture has to be built to heat each type of chip. Heating the chip can also alter the characteristics of the chip or the defect and should be avoided.
This invention deals primarily with microscope design techniques which reduce the parasitic thermal radiation which will impinge upon the thermal detector element, and allows the construction of a microscope can detect thermal radiation emitted from chips at room temperature, without having to cool most of the optical components. This allows practically any complex optical configurations to be used, and significantly improves the quality of the analysis which can be performed.